Cases of osteofibrosis are not infrequently reported from race-horse stables where the animals are fed on cereal concentrates, and where the hay ration is kept relatively low. Unless legume hay is fed, or a collection is made in the diet by the supplementation of calcium, rations consisting for the most part of cereals may prove to have a high phosphorus and a low calcium content. The occurrence of osteofibrosis has been reported from various countries, but has assumed a magnitude of considerable economic importance in India and the Philippine Islands, where the native feeds supplied to animals are relatively low in calcium. Although the disease is well known, the nomenclature used by different writers in describing it, differs considerably. The result is that a certain degree of confusion exists in regard to the various terms applied to this and related osteodystrophic disorders. An attempt was, therefore, made to produce cases of osteofibrosis in horses. The material collected would then form a useful basis of bone pathological omparisons in osteodystrophic diseases. (1) Clinical symptoms of osteofibrosis were brought about, and later definitely shown to be the disease by histo-pathological examination, in three 2-year-old fillies receiving a ration which contained 4 - 5 grams CaO and 54 - 29 grams P2 O3 in the case of two horses, and
28 - 42 grams P2 O5 in the case of the other horse. (2) The two control fillies received in their ration 52-· 3 grams CaO and 28- 42 grams P2 O5. The CaO intake had necessarily to be
high in order to rectify the otherwise abnormal CaO: P2 O5 ratio. (3) The control animals gained in weight, whereas the horses receiving a deficiency of CaO in their diet lost weight, became
emaciated and poor in condition. (4) Balance trials showed that the skeletons in the case of those
horses receiving 4 · 5 gms. CaO, were continually being depleted of calcium. (5) The phosphorus retention was greatest for the horses receiving most phosphorus in their ration. (6) From the data available it would appear that blood Ca determinations are of little value for diagnostic purposes in cases of suspected osteofibrosis. (7) Facial enlargements, when once established by the disease,
were not reduced in size by feeding a ration which was supplemented with CaCO3
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